The present invention relates generally to methods for manufacturing intraoral radiographic film packets with comfort enhancing features, and, in particular, to improvements to intraoral radiographic film packets which allow for ease of manufacture and subsequent operations such as the application of a comfort-enhancing perimetric edge bead.
A common problem experienced by people visiting the dentist is the discomfort and pain associated with the taking of dental x-rays caused by the positioning of intraoral radiographic film packets in the patient""s mouth. The typical intraoral radiographic film packet includes relatively hard and/or relatively sharp edges that press against and irritate the gums and other oral soft tissue of the person whose teeth are being x-rayed. A variety of intraoral x-ray dental packets are known in the prior art which include features intended to be comfort enhancing. In addition, attempts have been made to create comfort enhancing structures into which intraoral x-ray dental packets can be inserted prior to placement in the patient""s mouth. One example of this type of structure is taught in U.S. Pat. No. 5,044,008 titled xe2x80x9cDental Film Cartridge Cushion,xe2x80x9d by Reginald B. Jackson, Aug. 27, 1991. Jackson utilizes a cartridge cushion comprising a foam sheet sandwich into which the x-ray dental packet is placed for the purpose of cushioning and increasing the comfort to the patient. Jackson requires the manual insertion of the x-ray packet into the cartridge cushion. Thus, Jackson adds significant bulk to the packet and enhances the possibility of triggering a gag reflex action in the patient. Additionally, after the cartridge cushion is removed from the packet, it would be possible to reuse the cartridge cushion which would not be sanitary.
A second example of an add-on structure is taught in U.S. Pat. No. 5,285,491 titled xe2x80x9cDental Film Packet,xe2x80x9d by Muylle et al., Feb., 8, 1994. Muylle et al. teaches sealing a film pack in an envelope consisting of a pair of thin pockets of injection molded plastic which are sealed with a band of adhesive tape. The envelope has no sharp edges and generally rounded corners. Thus, as with Jackson""s device, this device requires manual insertion of the packet, adds significant bulk to the packet, enhances the possibility of triggering a gag reflex in the patient, and can also be reused in a non-sanitary manner.
U.S. Pat. No. 1,631,497 titled xe2x80x9cDental X-ray Film Package,xe2x80x9d by Harry L. Marler, Jun. 7, 1927 teaches a dental x-ray film package wherein a sensitized sheet is sandwiched between two opaque sheets. A heavy band of rubber is stretched about the periphery of the package to hold the package securely together and to provide the light-tight joint.
U.S. Pat. No. 1,537,925 titled xe2x80x9cDental X-ray Film Package,xe2x80x9d by Leonard M. Bolin, May 12, 1925, teaches a dental x-ray film package wherein a pair of film sheets and the cover sheet are inserted into the container. The container consists of a frame including a backing portion in an enlarged continuous beading about the periphery thereof. The beading must be forced away from the backing portion and stretched peripherally in order to insert the film sheets and cover sheet therein. The container thus serves to hold the package together and provide the light-tight seal.
U.S. Pat. No. 4,791,657 titled xe2x80x9cIntraoral Radiographic Film Packet,xe2x80x9d by Alan Kirsch et al., Dec. 13, 1988, teaches a dental radiographic film packet which includes soft corners for greater patient comfort. The packet is constructed by removing all material from the corners of a typical dental radiographic film packet with the exception of the film chip. Individual corner covers which are seamless pockets are then added to the four corners of the packet. The corner covers create an airspace at each corner around the edge of the film chip.
U.S. Pat. No. 2,084,092 titled xe2x80x9cDental Film Holder,xe2x80x9d by Ralph Kenney, Jun. 15, 1937, teaches a dental film holder that is a stretchable vellum rubber plate with integral corner pockets into which an x-ray dental packet may be manually inserted. Kenney""s dental film holder is intended to be reusable. The plastic envelope of an intraoral dental radiographic film packet of the type disclosed in U.S. Pat. No. 3,443,093 titled xe2x80x9cDental X-ray Packet Having A Uniform Overall Thickness And Method Of Making Same,xe2x80x9d by Terry N. Lindenmuth et al., May 6, 1969, is typically constructed by joining at the margin thereof two generally parallel sheets of flexible plastic material (typically flexible PVC). Two webs of plastic (which may be referred to as the base and top webs) form the envelopes of the dental film packets. The dental film, lead and opaque sheets are inserted and deposited on the base web and the top web is placed there over. The top and base webs are then sealed at the margin of the each packet to form a continuous web of sealed packets. The continuous web of sealed packets is subsequently die-cut to form a plurality of individual film packets.
Any subsequent operation requiring accurate positioning of the individual film packets, such as for the purpose of molding a compliant bead as disclosed in U.S. Pat. No. 4,912,740 titled xe2x80x9cIntraoral Dental Radiographic Film Packet Improvement,xe2x80x9d by Elmer W. Liese, Jr. et al., Mar. 27, 1990, becomes very difficult due to several factors including: a) size variation resulting from the die-cutting of flexible material with residual web stress; b) deflection of the marginal area (laminated perimetric edge) of individual film packets (the marginal area does not remain planar after the die-cutting operation); c) the flexible nature of the laminated perimetric edge when placed in a positioning fixture; and d) poor encapsulation of the perimetric edge due to easy and randomized deformation of the marginal area.
From the foregoing it can be seen that many attempts to add a comfort enhancing feature to dental x-ray film have packets resulted in structures requiring manual assembly and/or modification of individual film packets in order to receive comfort enhancing structure. Further, such prior art attempts, particularly those seeking to provide the comfort enhancing feature via a frame, have resulted in a significant increase in bulk thereby enhancing the possibility of inducing a gag reflex, and/or also resulted in a structure in which additional manual steps are required for assembly and/or disassembly. Also, the prior art designs fail to provide the features and operations that allow for automated, accurate positioning of individual film packets for automated application of comfort enhancing features thereto that overcome the problems of size variation resulting from the die-cutting of flexible material with residual web stress, deflection of the marginal area of individual film packets, and the flexible nature of the laminated perimetric edge when placed in a positioning fixture for application of a comfort-enhancing perimetric edge bead.
It is therefore, an object of the present invention to provide a method for manufacturing an intraoral dental radiographic film packet that includes a semi-rigid envelope that permits accurate positioning for the purpose of performing subsequent manufacturing operations.
It is another object of the present invention to provide a method for making a dental film packet wherein the size of the packet is not affected by residual stress in the marginal area after die-cutting a continuous web of sealed dental packets into individualize dental packets.
Yet another object of the present invention is to provide a method for making a dental film packet wherein the packet is easier to accurately position for subsequent operations such as the application of a comfort-enhancing edge bead.
Still another object of the present invention is to provide a dental film packet that is resistant to deformation when placed against a positioning device for subsequent operations such as the application of a comfort-enhancing edge bead.
The foregoing and numerous other features, objects and advantages of the present invention will become readily apparent upon a review of the detailed description, claims and drawings set forth herein. These features, objects and advantages are accomplished by forming an intraoral dental film packet with an envelope comprised of two outer plastic sheets wherein preferably one of the two outer plastic sheets is a stiffening sheet. The stiffening sheet is more rigid than the typical outer sheets found on prior art dental film packets. The stiffening sheet preferably has a tensile modulus in the range of from about 700 to about 28,000 Kg/cm2. The envelope is formed by joining together the two outer plastic sheets at the marginal or peripheral area to form a perimetric laminated edge that preferably has a tensile modulus in the range of from about 400 to about 28,000 Kg/cm2. By making one of the outer sheets more rigid than the other, the laminated perimetric edge formed by bonding the two outer sheets together is substantially coplanar with the more rigid of the two outer sheets. This resultant rigidity of the film packet in combination with achieving a planar surface on one side of the packet enhances the ability to die cut the packet and maintain outside dimension tolerances. Further, the rigidity obviates the easy deformation of the perimetric edge during subsequent operations in the handling and positioning of individual film packets after the die-cutting operation. This, in turn, allows for more accurate positioning of individual film packets in such subsequent operations. In addition, the planarity of the laminated perimetric edge also aids in achieving full encapsulation by peripheral edge bead. After die cutting there is likely to be some limited deflection (curling) of the laminated perimetric edge away from the plane of the stiffening sheet as a result of the stress exerted by the opposite outer sheet. This limited deflection is still substantially coplanar as compared to the prior art dental film packets. As used herein, the term xe2x80x9csubstantially coplanarxe2x80x9d means that deflection of the laminated perimetric edge away from the plane of the stiffening sheet after die cutting is no more than about 20 thousandths of an inch and preferably no more than about 10 thousandths of an inch.
In the practice of the method of the present invention individual film packets are transported by a Bernoulli effect apparatus against hard stop reference points. The added rigidity of the laminated perimetric edge and the concomitant improved outside dimensional tolerances achieved therewith allow individual film packets to be transported by a Bernoulli effect apparatus and hard stop reference points without deformation of the laminated perimetric edge. In such manner, individual film packets can be accurately positioned for subsequent operations including acquisition by a robotic arm for insertion into an injection molding apparatus for the formation of a peripheral edge bead on the packet. The improved planarity and outer dimensional tolerances of the film packet assure not only that the film packet can be accurately positioned but also that the die-cut edge will be fully encapsulated with the application of the injection molded perimetric edge bead. The positioning of individual film packets against hard stop reference points by a Bernoulli effect apparatus results in a force being applied to the laminated perimetric edge of the film packet in a direction which is substantially parallel to the plane of the stiffening sheet. The laminated perimetric edge should have sufficient rigidity such that it will not deform when these forces are in the range of from about 5 to about 80 millinewtons (the level of force likely to result from using a Bernoulli effect device to position the dental packet against hard stop reference points).